The present invention pertains to a device for cooling a symmetrical component of a turbine unit subject to high temperatures of nonuniform intensity over its circumference wherein the wall of the component is exposed to a hot medium on one side and is cooled on the other side by a flow of cooling air guided along that side.
Such components are provided in various areas in gas and steam turbine units. A special application is the two-armed gas collection pipe, also called bifurcated pipe, which is provided with two inlet pipe branches and is arranged in gas turbine units between the combustion chamber housings and the inlet pipe branch of the turbine blades (DE-OS 198 15 473). Due to the special shape of the inlet pipe branches of this gas collector pipe, the middle areas in its outlet cross section are subject to substantially higher thermal stress than the upper and lower areas.
The outlet cross section is cooled by cooling air being guided along the side facing away from the hot gas. This cooling air is taken from the compressor of the gas turbine unit. In a gas turbine unit known from practice, the amount of cooling air is limited by slots, which are arranged in the ring-shaped inner flange of the gas collector pipe, which flange joins the companion flange of the turbine. These slots are arranged distributed uniformly over the circumference of the inner flange in the prior-art gas turbine unit. Due to the asymmetric exposure to temperature due to the hot gas flows arriving from the two combustion chambers in combination with the symmetrical distribution of the cooling air, the material temperature will be nonuniform in the circumferential direction at the inner flange of the gas collector pipe. However, the service life of such components subject to high temperatures is determined by the maximum material temperatures occurring, so that the zones with markedly lower temperatures do not have a favorable effect on the service life. This means that the service life potential is lost because of the nonuniform temperature distribution. Moreover, the nonuniform temperature distribution on the circumference may lead to warping and bulging.
The basic object of the present invention is to make uniform the cooling of components of this type which are subject to nonuniform thermal stress without extra cost.
According to the invention, a device is provided for cooling a symmetrical component of a turbine unit, which component is subject to nonuniform stress over the circumference due to high temperatures. The wall of the component is exposed to a hot medium on one side and is cooled on the other side by a flow of cooling air guided along that side. A ring protrudes into the flow of the cooling air and is provided with slots or other openings for the passage of the cooling air. The ring is connected to the component. The overall cross section of the slots arranged in sections of the ring that are adjacent to the areas of the component that are subject to the higher stress is larger than the overall cross section of the slots that are arranged in the sections of the ring that are adjacent to the areas of the component that are subject to a lower stress.
The slots in the ring may be arranged distributed nonuniformly over the circumference of the ring. A distance between the slots may be smaller in the sections of the ring that are adjacent to the areas of the component that are subject to the higher stress. The slots may have different widths over the circumference of the ring. In such case, the width of the slots is greater in the sections of the ring that are adjacent to the areas of the component with the higher stress.
The intensity of the convective cooling by the cooling air in the outlet cross section is determined by the velocity and the amount of the cooling air that flows along there. To ensure the flow of cooling air in the first place, a pressure difference xcex94p is necessary over the slotted, ring-shaped inner flange. The cooling air flows through the slots arranged on the circumference of the inner flange. The geometry of the slots themselves as well as their arrangement thus directly affect the amount and the distribution of the cooling air due to the distribution on the circumference. The ring-shaped inner flange of the component thus represents the throttling member for the amount of cooling air. A directed, nonuniform, but adapted flow distribution can thus be achieved in the outlet area of the component solely by the arrangement and the geometry (size) of the cooling air slots. This adapted flow distribution is possible without the use of baffle plates or chambers. This is a simple restricted flow guidance by correspondingly setting the geometry of the throttling member for the outlet of the cooling air.
It should be emphasized in particular that the overall area of the cooling air slots is not changed, i.e., the amount of cooling air is not increased, either. The cooling air, which normally cools areas that have only a low temperature stress, is led by this measure to the areas which are subject to a higher temperature stress. As a result, the material temperature of the outlet cross section increases in the cold zones. However, the temperatures drop in the two hot zones, so that a nearly uniform temperature profile is obtained over the circumference.
The advantages arising from the measures according to the present invention comprise a reduction in the local, service life-limiting material temperature, the temperature distribution becoming more uniform, a reduction of temperature stresses, an improvement in the temperature and corrosion resistance, and an increase in the service life of the component.
Another advantage is that an increased cooling air demand is not necessary. Additional cooling air is usually supplied for the hot zones in the methods known and used hitherto to eliminate temperature peaks in components subject to high temperature stresses. However, this additional cooling air is usually not available, or it leads to a reduction in the efficiency of the turbine.